Orthopedic joint replacement and stabilization surgery has grown in popularity over the course of the last several decades. Advances in technology have made procedures such as hip replacement, knee replacement, and bone stabilization commonplace. Joint replacement procedures typically involve replacing a damaged joint with a prosthetic implant that is shaped in a way that allows movement similar to that of a healthy joint. Stabilization procedures typically involve bracing or fixating an injured bone so that it heals properly. Implants used in both types of procedures may be made from metal, plastic, ceramic, or some other substance.
In order for an orthopedic replacement procedure to be successful, a physician must be able to anticipate both the type and size of implant needed. Doing so reduces the risk of complications during the procedure, including nerve injury, instability, intraoperative fracture while inserting the implant, postoperative pain, and even failure to have the correct hardware available. Use of a proper implant also enables the procedure to be performed safely and accurately, providing strong fixation between implant and bone. Thus, being able to anticipate both the type and size of the implant is desirable to ensure the procedure's success.
Traditionally, a physician would manually size implants to radiographic (i.e., x-ray) images of the patient's joint and the associated bone structure. The physician would place a clear sheet, or template, containing an outline in the shape of the implant over the radiograph. This outline may include points, solid lines, dashed lines, or dotted lines, at least some of which may correspond to common bone structure or physiological reference points. Given that radiographic images are typically magnified by approximately 10% to 25%, the template is also typically magnified to account for the anticipated magnification of the patient's bone structure when a radiograph is taken.
The physician could then line up the template to a section of the patient's bone structure. By using multiple templates of different sizes in essentially a trial-and-error procedure, the physician would eventually determine a size for the actual implant hardware. However, this method is often inaccurate due to an inherent weakness. Traditional templates can only provide one magnification. As a result, it is usually an average for the entire population. Yet, magnification in the general population varies widely as it is proportional to body habitus. For example, extremely large patients have much greater magnification on their radiographs than small patients. As a result, this traditional procedure is subject to the risk that an implant of the wrong size will be used.
In order to overcome this problem, some physicians place a sizing marker on the radiograph which enables them to more accurately determine the magnification of the radiograph. Once the radiograph has been templated, the physician then adjusts the final result by the determined magnification. This method ultimately fails because the template is not resized to the correct magnification before being placed over the radiograph. As a result, the incorrectly sized template is placed in the incorrect position. Unfortunately, any template in the incorrect position cannot accurately determine the size of implant hardware needed. Therefore, using a magnification marker for traditional templating does not improve the accuracy of the templating process.
To improve the accuracy of traditional templating, many physicians now use digital templating. With digital templating, the physician views the radiographic image on a computer, and uses a computer representation of the template to attempt to fit the template to the bone to be replaced or stabilized. Digital templating has a significant advantage over traditional methods in that digital templates are not limited to one size magnification. Templating software enables either the templates or the radiograph to be adjusted to the correct magnification prior to placement of the template. Nonetheless, while digital templating addresses some of the problems of orthopedic templating, current systems have several disadvantages, in that they are proprietary, inflexible, prohibitively expensive, difficult to set up and maintain, and hard to use.